#include <bits/stdc++.h>
#define SZ(x) ((int)x.size())
#define all(x) x.begin(), x.end()
#define uni(x) sort(all(x)), x.erase(unique(all(x)), x.end())
#define fi first
#define se second
#define FOR(i, a, b) for (int i = a, _b = b; i <= _b; ++i)
#define FORD(i, a, b) for (int i = a, _b = b; i >= _b; --i)
#define FORLL(i, a, b) for (ll i = a, _b = b; i <= _b; ++i)
#define FORDLL(i, a, b) for (ll i = a, _b = b; i >= _b; --i)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define dbg(...) debug(#__VA_ARGS__, __VA_ARGS__)
template<typename T>
void __print_one(const char *&s, const T &x)
{
while (*s == ' ') ++s;
const char *p = s;
int bal = 0;
while (*s)
{
if (*s == '(') ++bal;
else if (*s == ')') --bal;
else if (*s == ',' && bal == 0) break;
++s;
}
cerr.write(p, s - p) << " = " << x;
if (*s == ',')
{
cerr << " , ";
++s;
}
}
template<typename... Args>
void debug(const char *s, Args... args)
{
cerr << "[ ";
int dummy[] = {0, (__print_one(s, args), 0)...};
(void)dummy;
cerr << " ]\n\n";
}
template<class X>
bool maximize(X &a, X b)
{
if (b > a)
{
a = b;
return true;
}
return false;
}
template<class X>
bool minimize(X &a, X b)
{
if (b < a)
{
a = b;
return true;
}
return false;
}
// -----------------------------------------------------------------------------------------
constexpr int maxn = 505, MOD = 1e9 + 7;
int n, A[maxn], B[maxn], inv[maxn], C[maxn][maxn], fact[maxn];
vector<int> vecPoint;
vector<pii> intervals;
ll dp[maxn][2 * maxn + 5], F[2 * maxn + 5][maxn];
// -----------------------------------------------------------------------------------------
void readInput()
{
cin >> n;
FOR(i, 1, n)
{
cin >> A[i] >> B[i];
vecPoint.push_back(A[i]);
vecPoint.push_back(B[i] + 1);
}
}
int binpow(int a, int b)
{
int res = 1;
for (; b; b >>= 1, a = 1ll * a * a % MOD)
if (b & 1) res = 1ll * res * a % MOD;
return res;
}
void preprocess()
{
fact[0] = 1;
FOR(i, 1, n)
fact[i] = 1ll * fact[i - 1] * i % MOD;
inv[n] = binpow(fact[n], MOD - 2);
FORD(i, n - 1, 0)
inv[i] = 1ll * inv[i + 1] * (i + 1) % MOD;
uni(vecPoint);
intervals.push_back({-int(1e9), -int(1e9)});
FOR(i, 0, SZ(vecPoint) - 2)
intervals.push_back({vecPoint[i], vecPoint[i + 1] - 1});
// for (pii p : intervals)
// dbg(p.fi, p.se);
FOR(i, 0, n)
{
C[i][0] = C[i][i] = 1;
FOR(j, 1, i - 1)
C[i][j] = (C[i - 1][j] + C[i - 1][j - 1]) % MOD;
}
FOR(i, 1, SZ(intervals) - 1)
{
int len = intervals[i].se - intervals[i].fi + 1;
FORD(CNT, n, 1)
{
int curC = 1;
FOR(k, 1, min(CNT, len))
{
curC = 1ll * curC * (len - k + 1) % MOD;
F[i][CNT] += (1ll * curC * inv[k] % MOD * C[CNT - 1][k - 1] % MOD);
}
F[i][CNT] %= MOD;
}
}
}
bool cover(int i, int j)
{
return intervals[j].fi >= A[i] && intervals[j].se <= B[i];
}
void solve()
{
dp[0][0] = 1;
FOR(i, 1, SZ(intervals) - 1)
dp[0][i] = 1;
ll res = 0;
FOR(i, 1, n)
{
FOR(j, 1, SZ(intervals) - 1)
{
if (cover(i, j))
{
int CNT = 1;
FORD(k, i - 1, 0)
{
dp[i][j] += 1ll * dp[k][j - 1] * F[j][CNT] % MOD;
CNT += cover(k, j);
}
}
dp[i][j] += dp[i][j - 1];
dp[i][j] %= MOD;
}
res += dp[i][SZ(intervals) - 1];
}
res %= MOD;
cout << res;
}
signed main()
{
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
// #define TASK "TEST"
// if (fopen(TASK".INP", "r"))
// {
// freopen(TASK".INP", "r", stdin);
// freopen(TASK".OUT", "w", stdout);
// }
readInput();
preprocess();
solve();
return 0;
}
